Hydraulic cylinder-servo controller



Oct. 14, 1958 J. E. BALLMER HYDRAULIC CYLINDER SERVO CONTROLLER Filed July 1, 1957 N -I" N INVENTOR. dflfl's 5 amume nited States 2,855,902 HYDRAULIC CYLINDER-SERVO CONTROLLER Application July 1, 1957, Serial No. 669,087

6 Claims. (Cl. 121-41) This invention relates to hydraulic actuating cylinders, and particularly to servo-controlled cylinders in which an extensible piston or the like automatically takes up and maintains a position corresponding to and as defined by the extent of motion represented in an input control or signal.

An object of the invention is to present a hydraulic actuating cylinder of the kind described which is simple, light in weight and all mechanical in its construction and operation.

Another object of the invention is to present a cylinder of the kind described in which all of the operating parts of the cylinder are contained within the cylindrical housing, there being external to the device only the laterally projecting means to provide the input signal.

A further object of the invention is to utilize generally new means to provide the feed back signal including a pair of racks and differentially geared pinion means carried by the piston.

Still another object of the invention is to introduce a new principle in cylinders of the kind described having as a feature thereof a cam supported for rotary and bodily shifting movements and transforming one to the other to obtain adjustment of a spool valve for control of the flowing pressure fluid.

Other objects and structural details of the invention will appear from the following description when read in connection with the accompanying drawings, wherein:

Fig. 1 is a view in side elevation, broken away, to show the valve mechanism in a partly diagrammatic form and the means for adjustment thereof;

Fig. 2 is a view similar to Fig. 1, showing the piston and the rack and pinion mechanism which provides the feed back signal;

Figs. 3, 4 and 5 are views in cross section, taken along respective indicated lines as shown in Fig. 2; and

Fig. 6 is a detail view in plan of the mounting for the cam means comprising a part of the mechanism for delivering the input signal.

Referring to the drawing, a servo-controlled hydraulic actuator in accordance with the illustrated embodiment of the invention comprises a cylinder 10 open at its ends. In one end of the cylinder 10 is stationarily installed an end wall 11. Received in the other end of the cylinder, and releasably locked therein in a convenient manner, is a valve body 12. A spacer element 13 is disposed within the cylinder intermediate the end Wall 11 and the valve body 12. The adjoining faces of the spacer element 13 and the end wall 11 are formed with respective circular grooves 14 and 15. A longitudinally disposed rod 16 has its ends received in the opposing grooves 14 and 15 and serves to maintain a predetermined spaced apart relation between the end wall 11 and spacer 13, with the latter in contact with the inner end of valve body 12. The construction and arrangement of parts serves further to prevent longitudinal motion of the rod 16 relatively to the cylinder and to the parts 11 and 13.

The cylinder 10 mounts a piston assembly comprising a piston head 17 slidably received within the cylinder between the elements 11 and 13, and a rod 18 which extends longitudinally from the cylinder by way of a central opening in end wall 11. The outer end of the rod 18 is adapted to be connected to a part to be actuated.

The piston head 17 has a longitudinal, laterally offset opening through which the rod 16 extends. In its longitudinal axis it also is formed with a central recess 19 opening through the head 17 and longitudinally into the rod 18 in which is relatively slidinglyreceived another rod 20. Still further formed in the piston head 17 is a laterally opening recess 21 in tangential relation to the longitudinal axis of the head. Received in the recess 21 is a unitary pinion assembly 22 comprising spaced apart pinions 23 and 24 and an intermediate bearing member 25. The aforementioned rods 16 and 20 are substantially circular in cross section. A part of their respective surfaces are formed with longitudinal rows of teeth adapted to mesh with the teeth on the pinions 23 and 24. The rods 16 and 20 thus have the character of racks longitudinally traversed by the pinions 23 and 24. The pinions 23 and 24 have an unequal number of teeth. The result of a movement of the pinion assembly 22 over theracks 16 and 20 accordingly is to effect a relative longitudinal adjustment of the rack 20. The rack 16, being held against longitudinal motion, serves as a track. The motion necessarily resulting from the inequality of teeth on the pinions 23 and 24 accordingly is achieved in the rack 20 which has a relative sliding motion in the piston assembly.

The outer end of the rack 20 is reduced in diameter to form a projecting portion 26 which is received in one end of a tubular sleeve 27. The opposite end of the member 27 is closed by a flat, head-like formation 28. A compression spring 29 is mounted between the head 28 and a flange on a bushing 31 which receives the described one end of the member 27 in telescoping relation. The parts are interconnected by a cross pin 32 which extends transversely through the rack extension 26 and into the bushing 31, passing through a longitudinally elongated slot 33 in the sleeve 27. The assembly comprising the rack extension 26, member 27 and sleeve 31 extends through the cylindrical spacer element 13 in a manner substantially to project the outer planar surface of the head 28 into a chamber 34 formed as a recess in the inner end of the valve body 12 and in effect surrounded by a circumferential projection 35 on the body 12. A portion of the chamber 34 is formed as a cylindrical recess 36. Another portion, in vertically spaced apart, opposed, relation to the cylindrical recess 36 is formed as a generally rectangular recess 37.

A cam sleeve 38 is transversely disposed in the chamber 34 to have its opposite ends received in respective recesses 36 and 37. One end thereof has a bulbous or cylindrical formation to interfit with the wall of recess 36 whereby the cam sleeve is restrained from relative axial motion but may move in a rotary sense and in a lateral or longitudinal sense relatively to the recess 36. That end of the cam sleeve 38 opposite bulbous end 39 is formed with aninternally flanged portion 41 in which is a pair of diametrically opposed slots 42.

The cam sleeve 38 surrounds a hollow shaft 43 which is introduced into the body 12 by way of a lateral opening 44 normally closed by a thrust button 45. The shaft has an open end resting on the thrust button 45. At its other end, the shaft terminates in a cylindrical head portion 46, beyond which is a guide pin portion 47 received in a complementary opening in the valve body. The spherical portion 46 of the shaft is in the installed position of the parts received in and laterally aligned with the flange 41 on the cam sleeve 38. The exterior of the portion 46 is in contact or substantially in contact with the inner surface of the flange 41. A cross pin 48 is mounted in the spherical portion 46 and projects therefrom into the diametrically opposed slots 42 in the cam sleeve. Any suitable means may be provided for rotating the "shaft 43. In the illustrated instance, an extension 49 thereof has a pin in slot connection with the-shaft properand extends throughthe thrust button 45 and laterally through an opening in -the cylinder to the exterior of the device. It is'the're accessible for manual or suitable automatic operation to be rotated about its axis in either direction. Since the actuator 49 is connected to the shaft 43 for unison rotation, and since the latter is connected to the sleeve 38, through the cross pin 48, similarly for substantially unison rotary motion, the result of turning the member 49 rotatively about its axis is to effect a corresponding turning motion of the sleeve 38. Fixed to the-exterior of the sleeve 38 is a cam 51.

The cam 51 is a planar member, the edge of which comprises a concentric portion 52 and an eccentric portion 53. The edge of the cam is contacted by the head 28 of the sleeve 27 on rack 20. By virtue of the spring 29, the head 28 serves as a cam follower, and, as will be seen, as a comparatively stable reactant means providing a base for bodily shifting of the cam. Also engaging the edge of the cam 51, in opposed relation to the head 28, is one end of a spool valve 54 mounted in a recess 55 in the valve body 12. The valve 54 is urged outwardly into contact with the edge of cam 51 by a spring 56, relatively weaker than the spring 29. Through a longitudinal passage 57 and a lateral port 58, the rear of the recess 55 communicates with the chamber 34. The valve 54 accordingly is balanced so that its motion is not affected'by fluid pressure differences at opposite ends thereof. A hydraulic liquid under pressure is supplied to the valve body by way of a passage 59 therein. Communication with the low pressure side of the system is by Way of passage '61 in the valve body. The manner in which the valve 54 acts to control the flow of the pressure fluid to and from the cylinder on opposite sides of the piston head 17 is generally conventional. in a normal position of the parts as illustrated, the inlet passage 59 is closed, as are branches 62 and 63 of the outlet passage 61. Motion of the valve to the left connects the inlet passage 59 to an extension 64 thereof opening into the chamber 34 and thence into the upper part of the piston-cylinder portion of the device, or to the left of piston 'head 17 as viewed in the drawings. Simultaneously, a passage 65, communicating with the cylinder on the opposite or right hand side of the piston head 17 is commnnicated'with branch 62 of the outlet passage 61. Accordingly, a pressure difference is defined across the piston head 17 which causes the piston to move in the cylinder in a direction 'to extend the rod 18. Motion of the valve 54 in .the opposite direction from the position illustrated, will, of course have the opposite ef feet, with the fluid under pressure being admitted to the right of piston 17 and the space to the left thereof being connected to exhaust or to the outlet passage 61.

The described axial movements of the spool valve 54 are achieved by a bodily shifting movement of the .cam 51. Thus, rotary motion of the cam 51 in a counterclockwise direction from the position illustrated tends to be accomplished without compression of the relatively stiff spring 29. Accordingly, the result of such motion is in etfect to increase the overall length of means -2751 of the feed back mechanism whereby to shift the cam 51 laterally to the left as viewed in Fig. 1. The valve 54 is thereby moved as before described to admit pressure fluid to the left of piston 17 and to connect the space on the opposite side thereof to the low pressure'si'cle of the system. As the piston assembly moves in response to the pressure difference so established, the cooperative relation between the pinion assembly 22 and'the racks '16 and 20, as before described, effects an axial movement of the rack 20 to the right or in a direction to Withdraw the head 28 from the cam. The effective length of 'the cam is 4 shortened. The spring 56 causes the spool valve and the cam to follow the withdrawal of the rack 20 with the result that the parts resume the normal position illustrated and the piston assembly is substantially locked or maintained in the extended position which it achieved before the shutting off of pressure fluid to the cylinder.

For a return or retracting stroke of the piston assembly thecam 51 is turned in an opposite or clockwise direction. The spool valve thereby is permitted to move beyond or to the right of its neutral position as shown whereby to connect the space to the left of the piston head to the low pressure side of the system and to connect the space to the right of the piston head to the high pressure side of the system. Positive movement of the piston assembly in a retracting sense accordingly results. This movement is accompanied by a corresponding and proportional movement of the rack 20, in a reverse sense as compared with the previously described motion thereof, and the cam is by this means moved to restore the spool valve to its neutral position.

The spring loading of the follower or reactant means 28 makes it possible for the actuating cylinder to accept the maximum input signal instantaneously, without need to introducesuch signal in a step by step fashion in following relation to the movement of the piston assembly. Excess initial movement of the cam is absorbed in the spring 29, with the sleeve moving relatively to the rack 20 by virtue of the pin in slot connection 32-33. Movement of the rack 20 in response to the motion of the piston thus is without effect upon the sleeve 27 until the parts reach the normal position illustrated.

The travel of the spool valve 54 is limited to obtain the optimum pressure drop through the valve. A seat 66 in the bore 55 limits the movement of the valve in one direction. Motion thereof in the opposite direction is limited by a pin 67 eccentrically located in one end of a screw stud 68 installed in the valve body and accessible from outside the cylinder for rotary adjustment. The pin 67 projects into a circumferential groove 69 in the valve 54. As the screw 68 is turned it positions the spool axially. The valve travel can be varied by changing the diameter of the eccentric pin 67.

The circular grooves 14 and 15 which mount the ends of the rack 16 permit the piston assembly to be rotated, as may be necessary in connecting to an external part to be actuated, without disturbing the relationship between the rack and the piston.

What is claimed is:

l. A hydraulic actuator, including a cylinder, a piston reciprocable therein, a spool valve within said cylinder in longitudinally spaced relation to said piston and adjustable axially to control a flow of pressure fluid to said piston, cam means supported in said cylinder for rotary and bodily shifting motions, said cam means bearing on one end of said spool valve, reactant means contacting said cam means in opposed relation to said spool valve, rotary motion of said cam means effecting bodily shifting thereof on said reactant means to adjust said spool valve in a first sense, and means responsive to movement of said piston to effect a relative movement of proportional extent of said reactant means to adjust said spool valve through said cam means in an opposed sense.

2. A hydraulic actuator according to claim 1, characterized in that said last named means includes a relatively stationary rack, a rack connected to said reactant means, and pinion means in common engagement with said racks and carried by said piston, said piston means being differentially constructed to effect limited relative motion of the rack connected to said reactant means in response to motion of said piston.

3. A hydraulic actuator, including a cylinder, a piston reciprocable in said cylinder and extensible through one end thereof, a valve body installed in and closing the other end of said cylinder,.there being an internal chamber between said valve body and said piston, a spool valve slidable in said valve body to adjust for a flow of pressure fluid to said cylinder, one end of said valve extending into said chamber, cam means located in said chamber and supported therein for relative rotary and bodily shifting movements in the plane of said spool valve, spring means maintaining said spool valve in contacting relation With said cam means, reactant means contained within said cylinder and contacting said cam means in an opposing relation to said spool valve, and means extending laterally outside said cylinder to rotate said cam means, the rotary motion of said cam means being resolved into a bodily shifting motion thereof for corresponding adjustment of said spool valve.

4. A hydraulic actuator according to claim 3, characterized by means axially to move said reactant means for corresponding adjustment of said spool valve an extent in proportion to the movement of the piston, said last named means being contained Wholly within said cylinder.

5. A hydraulic cylinder according to claim 4, characterized in that said last named means comprises first and second racks installed longitudinally in said cylinder in independent relation to said piston, one of said racks being held against longitudinal motion relatively to the cylinder and the other being connected to said reactant means, and unitary pinion means carried by said piston including pinions having a diiferent number of teeth in engagement with respective racks.

6. A hydraulic actuator, including a cylinder, a piston reciprocable in said cylinder and extensible through one end thereof, a valve body installed in and closing the other end of said cylinder, there being an internal chamber between said valve body and said piston, a spool valve slidable in said valve body to adjust for a flow of pressure fluid to said cylinder, one end of said valve extending into said chamber, cam means located in said chamber and supported therein for relative rotary and bodily shifting movements in the plane of said spool valve, spring means maintaining said spool valve in contacting relation with said cam means, reactant means contained within said cylinder and contacting said cam means in an opposing relation to said spool valve, spring means superior in strength to the spring means acting on said valve resisting deflection of said reactant means in response to rotary motion of said cam means, excess rotary motion of said cam means being absorbed in said spring means acting on said reactant means, a follow up control contained wholly within said cylinder to move said reactant means in proportion to the motion of said piston, and means extending laterally outside said cylinder to rotate said cam means, the rotary motion of said cam means being resolved into a bodily shifting motion thereof for corresponding adjustment of said spool valve.

References Cited in the file of this patent UNITED STATES PATENTS 1,119,324 Sprater Dec. 1, 1914 1,500,685 Roberts July 8, 1924 1,742,946 Bertram Jan. 7, 1930 2,610,614 Sedgwick Sept. 16, 1952 FOREIGN PATENTS 307,817 Great Britain Mar. 14, 1929 

